If the brain has the wrong prior knowledge, our perception will be false. With modern technology we can make many novel pictures that the brain has not been designed to comprehend.We cannot avoid having false perceptions of these pictures. One object that it is almost impossible to perceive correctly is the inside of a hollow mask of a face. When we look inside this hollow mask, we cannot help but see it as a normal convex face. Our prior belief that faces are convex and not hollow is too strong to be modified. If the mask is slowly rotating, an additional illusion is caused. Because we see the mask inverted, the tip of the nose appears to be the nearest part of the face, when it is in fact the part that is furthest away. As a result we misinterpret the movement of the mask and see the direction of the rotation reverse whenever we are looking into the hollow.